1. Field of the Invention
The invention relates to the field of shut-off valves for use in connection with sprinkler irrigation systems.
2. Description of Prior Art
Sprinklers for irrigating recreational playing fields, golf courses, lawns and landscapes are often damaged by animals, accidents, mowers, vehicles, and vandalism. When a sprinkler irrigation system is turned on after such an accident, a considerable stream of water is lost where the sprinkler head or riser was damaged or severed. Since the water is no longer directed to the intended area by the sprinkler nozzles, little to no irrigation benefit is realized in the effected area. The amount of this excess flow can be three or more times the original flow rate through the sprinkler, reducing the overall operating pressure of the zone being irrigated. Therefore, the remaining sprinkler nozzles in the zone are not working with the designed uniformity or efficiency, resulting in uneven and inadequate irrigation. Until the system problem is noticed and repaired, water distributed at the damaged site usually runs off the intended area resulting in great wastage.
Since a great deal of sprinkler irrigation systems are operated automatically by an electric controller, any distribution problem will not likely be observed immediately. Consequently, the irrigation system will most likely continue operating for a number of cycles until physical evidence of a system problem begins to appear, such as the yellowing or wilting of lawns or landscapes.
The prior art solution is to provide a high volume shutoff valve in the irrigation system which will automatically shut down the line experiencing a high flow rate. The prior art discloses various structures for shutting off a valve when the valve encounters unusually high flow. High flow, however, exists not only in the instance of a damaged sprinkler head or severed riser, but also when a irrigation zone with empty lines is first started. This happens often when irrigation zones are free to drain to the lowest point between cycles, causing air to replace the draining water in the lines. Upon start up, pressured water pushes the air in front of it causing the air to both move rapidly at a high flow rate. Since air passes through the nozzles of sprinklers much more freely than liquid, the water advancing behind the air moves through the piping systems at velocities much higher than normal flow rates. Under the prior art, such high pressure of either the air or water, or both, resulting from the start-up of empty lines can trigger the high flow valve to shut off. Obviously, this circumstance is not what shut-off valves were designed for.
Therefore, what is needed is a valve which will shut off only in the case of high flow of water resulting from circumstances such as a damaged or removed sprinkler head or riser, but not when the irrigation system is first being started from empty lines. In other words, what is needed is an irrigation shut-off valve which will not give false shut-offs.